Thank you Maban.
I did some further research after my post and I completely agree with your recommendation. There are quite some articles showing that real life performance differences between playing at x8 or x16 PCI-E 2.0 are unnoticeable. Specially when my monitor max res is 1600x1200.
And yes, I came with the same reasonably priced mobo alternative, the WS Revolution, but given the above and the fact that I was going to perform at x16 over the NF200 chipset anyway (not native support) I decided to stay with the Asrock.
The good part is that I was overlooking an alternative case airflow arrangement which looks promising: CPU fans intake facing case front (not PCI-E slots, hence allowing me to use PCIE2) + top case fan as intake (not exhaust). This combined with side and bottom intakes (the only exhaust being rear fan right after CPU) can work very well. I plan to benchmark both fan configs.