Arctic Silver 5 is not a good paste to use with a newer modern cpu. At one time Arctic Silver 5 was the King but times have changed, get some Tuniq TX-2 and only use a gob about the size of a single grain of rice. Put the gob of paste in the center of the heatspreader and let the weight of the heat sink spread the paste.
Newegg.com - Tuniq TX-2 Cooling Thermal Compound
To much paste is worse than to little, it maybe hard to believe but it's True.
And the Zalman CPSN10 Extreme cooler was a huge waste of money, it's way overpriced and it will Never Equal a TRUE or the Prolimatech. I have a few TRUE's for sale when you decide to switch.
FS (3) Thermalright Ultra eXtreme 120 (TRUE)
As for Bottlenecking. No your CPU isn't bottlenecking your GPU. But your GPU could be considered a bottleneck for the i7 920 and above. But I'm really knit-picking. I say it's a bottleneck because your CPU has the power to run (2) GTX 480's or (2) 5870's and your limiting it's full potential with a 5770. Don't get me wrong, a better way to look at it is, you have more upgrade potential