Thermal shutdown is not normal and suggest either dried up thermal grease, dust bunnies, or the heatsink isn't seated properly on the CPU. Check out your local online PC store for replacement fans.
I'd keep the dual 1.25, and buy a single 1.25 (looks like you might be lucky seeing your WTB). I fixed up a single 1Ghz MDD for a friend recently, and it really was a lot slower than I'd expected running 10.5 (2GB RAM, Geforce 6800 PC flashed graphics card, fast 7200RPM HD). Noting you can get dual 1.42s off eBay very cheaply, I suggested my friend spend $30 - 50 on one of these should he find it getting painfully slow for day-to-day tasks.
JB
I'd keep the dual 1.25, and buy a single 1.25 (looks like you might be lucky seeing your WTB). I fixed up a single 1Ghz MDD for a friend recently, and it really was a lot slower than I'd expected running 10.5 (2GB RAM, Geforce 6800 PC flashed graphics card, fast 7200RPM HD). Noting you can get dual 1.42s off eBay very cheaply, I suggested my friend spend $30 - 50 on one of these should he find it getting painfully slow for day-to-day tasks.
JB