Yet another of the "Warmongering is the only way to go from CIII" nerfing in CIV that drives pure warmongers up the wall...
I generally research at the lowest percentage that makes slow money (after, of course, spending my Goodie Hut stash at first). This money slowly accrues, until the point where I reach an upgrade. I then sell a few techs for the extra cash, and upgrade.
The reason this works is, I'm not upgrading a huge warmongering army of death in most cases... my units are either working (attacking and dying), or garrisoning. And the trick is... don't upgrade the whole garrison.
For example, in my current Monarch game, I have a decent sized continent to myself... I have a small force of fast defenders at either end of the continent, and each city has 3 defenders -- 2 garrison units, and a fast counter-attacker. The trick is, LET that second tier garrison unit be not the latest and greatest.
For example... I build 2 archers to start with for garrisoning. Longbowmen come along... ONE per city gets upgraded. The other one stays an archer. Gunpowder comes along. The 2nd archer gets the upgrade... the longbowman stays a longbowman. Rifling comes along, the longbowman goes to rifleman, the musketman stays a musketman. Here comes assembly line, guess who's getting upgraded? I also do the same with my fast response units... the fast response stacks get one upgrade, the city fast responders get the next, etc.
Doing this, I've never had to reduce my research below 60% the entire game, and have been running at 80-85% for the last 200 turns or so. Is every unit the latest? No. But making it so cheap that upgrading and going to war becomes automatic was one of the failings of the series in the past, and I for one am glad to not see them repeating the mistake.