I would not give up on the big 250 mark yet
238MHz was stable with 1.7v correct? and temps were fluctuating between 55-58C.
I would attempt a run at 240MHz with a vcore of 1.71+ if it will stay below 60C. However you processor is actually rated for 75C of thermal output so you have some room. Keep it below or equal to 55C for 24/7 use but for a few hours test run it should be ok. This would allow you to see what settings work well and then purchase a better cooler to run those settings 24/7.
Make sure your memory operates as close to 400MHz as possible. Also burn in your processor at 238 first, so run Pirme95 or something that uses a huge amount of processing power for a long time to burn in the CPU at its current speeds. This may allow you to go a bit higher, it did for me
Make sure that the AGP/PCI values stay at 66.6MHz/33.3MHz or as close as possible all the way through.
Another point would be perhaps to increase the chipset voltage one notch to allow the data transfer to operate a bit better, this would make sure that its not the board that is limiting you
(very unlikely because the board is very good).