Caffeine sensitivity can drop very quickly. To me it takes about 200mg to notice much from caffeine. Maybe you've simply not tried high enough doses (be careful - caffeine withdrawal can get nasty)
I use modafinil quite regularly to defer sleep to work on projects through the night, and the difference from caffeine is very noticeable to me - to get the same effect from caffeine means jitters and noticeable increased heart rate.
Don't expect to get mental abilities above your normal rested self for either one of these. You should expect to be able to keep focusing for longer periods, including when tired, though.
More importantly to me than the immediate negative effects of caffeine is that I can take breaks from modafinil at any time, for any period of time, and feel no withdrawal. If I use large enough doses of caffeine to regularly make it through a night without sleep, and want to take a break from it, I need to step down my caffeine intake slowly or risk a week of intense headaches, diarrhoea, shakes in the evening, and fever.
I use modafinil quite regularly to defer sleep to work on projects through the night, and the difference from caffeine is very noticeable to me - to get the same effect from caffeine means jitters and noticeable increased heart rate.
Don't expect to get mental abilities above your normal rested self for either one of these. You should expect to be able to keep focusing for longer periods, including when tired, though.
More importantly to me than the immediate negative effects of caffeine is that I can take breaks from modafinil at any time, for any period of time, and feel no withdrawal. If I use large enough doses of caffeine to regularly make it through a night without sleep, and want to take a break from it, I need to step down my caffeine intake slowly or risk a week of intense headaches, diarrhoea, shakes in the evening, and fever.
Caffeine is nasty stuff...