What would be better water cooling or switching to Intel?

listen TW3 is almost perfectly multicored title, even at STOCK settings you won't be CPU bottlenecked with an FX8320, so an i5 won't help, your issue is the gtx970 won't hit 60fps in 1080p on ultra in TW3. TW3 is insanely hard on graphics cards to hit 60fps all the time in it, you need atleast a GTX980. That said i own TW3 and an i5 and a gtx970, i play TW3 in ultra settings, and only get 45-55 FPS in it. TW3 looks perfectly smooth over 30FPS for most people.

GTAV is buggy and choppy no matter what cpu you use, you could be using an 8 cored intel extreme edition overclocked to 5ghz and still get lag spikes durring play because it's fairly poorly optimized for multicores, but it IS a cpu intensive game. So there is some improverment to be found with an i5. That said you can get very very playable performance out of an FX 8 core just by overclocking it. I've been playing GTAV on my fx 8320 system, it plays fine. Of course my cpu is overclocked to 5.0 ghz; not a lot of FX 8 cores will hit that.

BF4 is a combination of two problems. problem one is BF4 is an AMD optimized title, and nvidia gpus seem to struggle playing it smoothly. Nothing can be done about that. Problem two is it's only a 3 core title, and it requires that fx 8320 to be overclocked up to 4.2-4.4 ghz to play smoothly.

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Now that i've explained your issues in those titles lets look at your options.

OVERCLOCK THE FX8320
-in order to overclock this cpu you'll need to replace two parts in your system
-one, the cpu cooler needs to be replaced in order to achieve an agressive overclock, something like the h100i GTX would be ideal
-two, the motherboard needs to be replaced, that asus m5a97 LE motherboard won't support any overclock, frankly it's probably at it's limits with your cpu at stock speeds. replace that motherboard with something like an asus m5a99x evo; check out the overclock validation in my sig, that's the board i used for that. No promises on the max overclocks you'll get with it, however you should at least get to 4.7ghz which should make GTAV playable.

PCPartPicker part list / Price breakdown by merchant

CPU Cooler: Corsair H100i GTX 70.7 CFM Liquid CPU Cooler ($104.99 @ NCIX US)
Motherboard: Asus M5A99X EVO R2.0 ATX AM3+ Motherboard ($99.99 @ SuperBiiz)
Total: $204.98
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-06-06 13:23 EDT-0400

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UPGRADE TO AN i5-4690k
-you'll need two parts, you should be able to use your current cpu cooler assuming you still have all the mounting brackets that came with it.
-buy an i5-4690k
-buy a z97 motherboard
-overclock the cpu to achieve desired performance in GTAV

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-4690K 3.5GHz Quad-Core Processor ($229.99 @ SuperBiiz)
Motherboard: MSI Z97-GAMING 5 ATX LGA1150 Motherboard ($136.98 @ Newegg)
Total: $366.97
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-06-06 13:24 EDT-0400

up to you on which option you want. either way you're going to need to learn how to overclock a cpu, or else you'll be disappointed with your purchases and game performance.