Save your money.
Sell and buy the 6-core 3.33GHz instead.
The SSD at least can go into any system but you won't benefit from it being 6G until there are SATA3 ports and by then new prices and models.
Amazon has 2 x 4GB for $220 top tier memory.as long as you have the slots the best DIMM configuration is to use all 8 slots.
We don't know when, we can guess and assume like every other new model that give it 3-4 months to work out firmware and chps and drivers and two OS patches though.. Buy yourself a good solid year and yours has value: it runs 10.5.8 or later and still fetches $1500 possibly making the Apple Store Special 2.8 4-core that can be upgraded $590 to same 6-core 3.33.
However - seems EVERYONE has done upgrades. that is not new different or unique and lots of threads. Take a look at those with 2008s - trouble with those models too with PSU or startup/shutdown and other oddities.
Use to be you could rely on and visit www.xlr8yourmac.com and find lot of reader feedback reports on systems.
I think the time to sell could be now.