Question about Upgrading Early 2008 Mac Pro Memory

I have an early 2008 Mac Pro running OS X Lion. It currently has 8GB of memory which consists of 4 memory modules of 2GB each, 2 on each of the memory cards.

I really want to go to 32GB but likely will go to 16GB. I do a lot of virtualization using VMWare often running Windows and Linux partitions so I think the additional memory will help a lot.

I plan to purchase from OWC which is where the memory I currently have is from but I see two options.

One is to buy 4 more of the 2GB memory modules which would then fill all slots and total 16GB and the total cost would be $241.

Another option is to buy 2 of the 4GB modules. The cost would be slightly more at $275.
-Would there be any advantages to this?
-Does it cause any issues and am I better off using all 2GB modules for example so that they match?
-One reason I prefer this option is although it costs slightly more if I'm correct that would leave 2 slots open where I could later upgrade with another 2 4GB modules for 24GB total.

Another option is am I better off (performance and price wise) simply starting over, getting all new memory. I can pay $549 and get 16GB (4 4GB modules) I know I could keep the current 8GB for 24GB total but again I don't think I need that much but I guess my question is, if I go with the 4 4GB modules and then get rid of the current 4 2GB modules would I get more performance using 4GB instead of 2GB modules. Also, I know OWC buys memory but I am assuming my best bet is eBay and if so, would I save money by getting the 4GB modules (4 of them) and then selling my current memory on eBay?

Thanks for your help with the above questions.

Mark

Can not see any advantage. I have same machine and upgraded to 22gig ram. Just as long as they are paired it will work fine... buy what you can afford..

My Mac Pro runs 8x2GB modules. Cannot answer question on performance other than to say OWC recommended eight identical modules give the best performance. Where you buy it is a matter of personal choice, but have great respect for OWC even with goods air mailed Down Under. Had one module fail, replaced by return air mail within seven days and of course f.o.c. with their lifetime warranty.