Good question! I didn't realise that a P55 based Mobo would work or be a good choice. There are so many options so it's a bit confusing.
I initially thought I'd go with the Gigabyte GA-H57M-USB3 because it had all the features I want and this Mobo also supports Clarkendale CPUs so I could potentially upgrade it at a later time without changing the motherboard. It also supports rapid storage which is an advantage. But the Gigabyte GA-H57M-USB3 is mATX board and I kinda prefer an ATX MoBo...
Could you please tell me why you think a P55 Mobo is better and which particular model you would recommend?
I'm not sure that I would consider the move from an i5 750 to a Clarkdale CPU an "upgrade". And in general any 1156 CPU (i.e. a Clarkdale or Lynnfield CPU) will work in any 1156 motherboard (i.e. chipset P55, H55, H57 or Q57). Of course you'll want to double check before making a purchase and some boards may require a BIOS update to support a particular CPU.
So which chipset to choose? Well, I always figured if you're getting a Lynnfield CPU then you'd want a P55 motherboard because the Lynnfield CPU's (i5 750, i7 860 and i7 870) don't have integrated graphics. Likewise if you got a Clarkdale CPU (any i3 or i5 6xx) you'd want a H55/H57/Q57 because the Clarkdale CPU's have integrated graphics and the H55/H57/Q57 boards support the graphics and give you on-board graphics capabilities. But using this one criteria as a determining factor may not be good for everyone. With an i5 750, you are going to have to get a graphics card, you cannot use the display-out options on the H55/H57/Q57 motherboards. But if you think in the future you are going use a Clarkdale CPU and not use a discrete graphics card then that might make sense.
The P55 boards also give more multi-card options. That is, you can find P55 boards with two GPU slots that will run in x8, x8 mode and are certified for SLI and CF. I have to date seen 1 H57 motherboard certified to run in x8, x8 but it can not run in that mode with a Clarkdale CPU, only a Lynnfield CPU and it was around $200. You can get a P55 that supports SLI and CF for less than that.
Now we'll try to answer a question which we asked four months ago: which chipset should you choose for a Socket 1156 processor? First of all, you must understand that incompatibilities between different chipsets and processors for this socket are not radical. Any of these processors will work in a motherboard with any of these chipsets. The question is whether you lose the integrated graphics which you have to pay for anyway. This seems simple: if you want to use Clarkdale's integrated graphics, take the H57. If you want a regular SLI/CrossFire, go with the P55 (note that by regular we don't mean "full-fledged dual x16"). However, you cannot have both. Now what about the most likely case, when you plan to use a single graphics card? In this case, there is absolutely no difference between the P55 and H57. Even chipset prices do not matter, since you will buy a ready motherboard, not a chipset alone. An H55-based motherboard may be a little cheaper though, but there may be no truly attractive motherboards with this chipset, I'm afraid. So you do have a choice, but there are no definite options worth paying more. On the whole, Socket 1156 processors seem to have decent chipset support.