Upgrading Motherboard + CPU

If you are worried about CPU-limitations, then you should go Intel. Something around a Z77 based board and an i5 depending on your budget should work for you. The Gigabyte Z77's are pretty cheap, although the ASUS Z77 series (I think the cheapest model is suffixed- LX) are very well reviewed everywhere.

Although you can OC your processor via the base clock (nomial 200 mhz, try 220 - 240 mhz for relativley pain free OC), if you have a good heatsink and case ventilation.

I've heard intel's are better. So i guess i'll be going towards that way then. I'm looking for something pretty powerfull, perhaps something just a little better than the 1055t, somewhere around the £150 for the Intel cpu?

Check your favourite local/online stores for the pricing in your region and currency. But I suspect for that amount of money, you can get an i5-3570k. That would be your best bet. It is unlocked, and very fast for games (and whatever else). If you don't plan to OC right away, you can stick with the stock heatsink for a while too. When you decide to OC, upgrade the heatsink (if you have an aftermarket one on your 1055t, you *might* be able to use that, to reuse).

As for boards, I would try the ASUS or MSI z77 series. For MSI, try the GD55 or GD65 series, both are easily affordable this side of the pond, so it just depends on your local pricing and discounts/sales/coupons, etc.

keeping within a 150/60 budget for cpu/motherboard:

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-3470 3.2GHz Quad-Core Processor (£145.38 @ Scan.co.uk)
Motherboard: MSI B75A-G43 ATX LGA1155 Motherboard (£56.10 @ Scan.co.uk)
Total: £201.48
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2012-12-09 16:12 GMT+0000)

going for the total of around 250:

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-3570K 3.4GHz Quad-Core Processor (£168.94 @ Amazon UK)
Motherboard: Asus P8Z77-V LX ATX LGA1155 Motherboard (£82.52 @ Scan.co.uk)
Total: £251.46
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2012-12-09 16:13 GMT+0000)

So this 3.2ghz quad-core is better than my 2.8 6 core processor? Though, that's due to games only using, at max, 4 cores right? I was thinking about getting a heatsink and oc my 1055t to 4ghz. Would this speed up some of my games, for example, guild wars 2 and so on that are cpu intensive?
Much appreciated.

Changing out a motherboard will not make your cpu any stronger.

I see no amd cpu upgrades that would be significantly stronger. For gamers, the bulldozer FX chips were a disappointment.
Here is one comparison of <$200 gaming cpu's.
The faster intel cores trumps the more numerous amd cores because games rarely use more than 2-3 cores:
http://www.tomshardware.com/reviews/gaming-fx-pentium-a...
The tests were done with a 7970 to eliminate graphics card limitations.

I would recommend an intel chip with a price that is about half the price of your graphics card for a good cpu/gpu balance.
If you go stronger on the cpu, that is OK because it allows for a future graphics upgrade.

Changing a motherboard will allow me to upgrade, as my motherboard will not support AMD3+, only up as far as AMD3 cpu cihps. And so i'm thinking about changing to a intel motherboard.

To test out the merits of a faster cpu, do some testing.

a) Run your games, but lower your resolution and eye candy.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration.
If your FPS stays the same, you are likely cpu limited.

b) Limit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 50%.
This will simulate what a lack of cpu power will do.

Go to control panel/power options/change plan settings/change advanced power settings/processor power management/maximum processor state/
set to 50% and see how you do.

If your FPS drops significantly, it is an indicator that your cpu is the limiting factor, and a cpu upgrade is in order.

That's right. But there are no AM3+ supported cpu's that are significantly faster for gaming.

if you can get that 1055t up to 4Ghz with just buying a heat sink then go for it. though the intel cpus , clock for clock, are better than any AMD; overclocking will compensate for that. to be honest, i am a little surprised you are having some problems with a 660ti and that cpu. so go through with the suggestions geofelt is posting - he is better at figuring that out than i.

if you find that after getting a heatsink and overclocking doesn't solve you problem, then atleast the heatsink can be used for an intel platform and look at getting a 3570K with a Z77/Z75 motherboard - you'll get set for anything after that.

That would be the most cost-efficient way. Get a heatsink that fits and works equally well on AMD and Intel (most anything decent these days will do), and when you upgrade, it gets transferred right over.

I did some research for you.
Read this article on guild wars 2. http://www.tomshardware.com/reviews/guild-wars-2-perfor...
It tests various cpu gpu clock rates, and core counts.
My conclusion is that your GTX660ti is as good as it gets for this game, and that the game is very cpu dependent.

It looks to me like the power of the individual cores is much more important than the number of cores.
On one chart, a sandy bridge dual core @3.0 is stronger than even a FX-8000 8 core cpu.

No doubt, you would do better overclocking your 1055T.
And the suggestion by looniam to buy a cooler is a good one. Just make certain that it also has a socket 1155 mounting kit.
But in the end, I don't think you will get great results without a 2500K class cpu.