Buying 20 Intel PCs for work to overclock to ~3.5GHz. What to buy?

[Ben70]

We are planning on upgrading about 20 PCs here where I work that are used by software developers. Compiling software is very CPU and hard disk (IO) dependent. The easy bit is to sort out the IO - we will be getting fast 128GB SSDs. The hard bit is the CPU, motherboard and memory.

Since these PCs will be used for work and need to be very reliable I want to overclock them moderately with *minimal fuss*. No extreme overclocking is required, but given compiling software is a CPU-limited task it makes sense to squeeze the performance out of the CPU because these new Intel CPUs are capable of it, and the high-end Intel CPUs are so expensive. Note also that compiling is not multi-threaded, so hopefully the Intel Turbo Boost technology should help quite a bit when compiling if we enable it.

I was thinking along the lines of:
1. Intel i920 CPU
2. Motherboard based on Intel X58 chipset
3. 3 or 6GB RAM (depends on whether we stay with 32-bit Windows XP or move to 64-bit Windows 7).
4. Heatsink? No idea if a high quality cooler is required for about 3.5GHz but it would be ideal if the stock CPU cooler could handle it.

Questions:
1. Is the i920 a good CPU to base this on? How easy is it to get an overclock in the 3 - 3.5GHz range (we can't afford to spend a long time with each PC, we'd want to determine good settings and then set them for all PCs with high confidence they all work well).

2. Given Intel Turbo Boost could help by 4-5 clock steps due to the single-threaded nature of the work load, would a simple i7-870 system be the way to go (2.93GHz default clock but 3.6GHz with 1 or 2 cores active)?

3. Recommendations on CPU coolers and memory also appreciated.