I bought the education base 2012 mini instead of the iMac that I was expecting to get. I've used it for a week with the stock 4GB ram, but one banking website in Safari would try and grab all 4GB. 'Safari Web Content' was going wild and giving the beach ball that you wished to avoid. I threw in a single 8GB stick (kingston KVR16S11/8 8gb 1600mhz ddr3 non ecc cl11) to give me a total of 10GB, and this improved things enormously with my banking website 'Safari Web Content' now grabbing 7.96GB ram! At least I had 2GB left to run the OS, which was enough - just about.
A quick Chrome browser d/l and the internet bank is fine, just not on Safari.
The moral of this - is that more ram is good, but bad software anywhere - anytime - can give you the beach ball!
My dual-core i5 mini CPU certainly behaves like it has 4 threads, activity monitor CPU shows quadruple indicators, I'm rarely pegging the CPU even when Safari is thrashing on a bad website. I can see that ANY quad i5/i7 in an iMac will work great, the extra magahertz will likely just add to global warming
The choice of 8GB or 16GB in the new iMac is a choice about what memory footprint you are likely to need in 2014 for OS10.9.x, are there any hints yet about the expected direction that Apple is going? thinner cloud client with bloatware
?? or massively parallel CPU/GPU processing
?? or everything triple AES encrypted?
??
if you get the base 21.5" iMac in 2 years you could always sell this late late late 2012 iMac with 8GB and get the thinner haswell 16 or 32Gb iMac option at that point if you *really* need more ram?
I think I'd actually suggest that you up your budget slightly to $1699 and buy from
http://store.apple.com/us-k12/browse/home/shop_mac/family/imac
as you must know someone, anyone in an education situation - $1699 then gives the 2.9GHz quad-core Intel Core i5, terabyte HDD, and the 8GB which you can upgrade next year yourself. The 27" screen is so much of an upgrade over the 21" that karmic happiness & enjoyment would be your reward. The extra screen real estate is very helpful for all your intended uses.
I suggest therefore that the real "base model" iMac is the base 27"