Ever since I stopped running competitively a little over a year ago, I've been lurking in this thread. I'm a big fan of all of the helpful info--kudos to you all.
Anyway, I've got a few questions about how the best way to vary lifting routines once it seems like strength is plateauing a bit.
A bit of background: Back in Nov. 2010, I was an absolute newbie to lifting. I used to run a LOT (usually over 100 miles a week), so I was incredibly skinny (just under 6'2", 135 lbs. or so). Then I started lifting. As one might expect, I made great gains at first, simply because I wasn't catabolizing everything with running. Recently my gains have slowed down a bit (I now weigh between 155 and 157), and I'm beginning to realize that I should be more methodical in my training regime. While I realize that I have the classic ectomorph build--and so won't be able to make HUGE gains--I think there's a lot more room for improvement.
I typically follow a four-day cycle: (1) chest/tris, (2) shoulders, (3) back/biceps, and (4) legs. I'll take a day or two off every month, and I run ~3 miles every other day. When I was starting out I would do three sets of most exercises with ten reps a set. A couple of months ago I started doing three sets of exercises at five reps a set. My goals are size and strength (I'd like to get up to 160-165), while still maintaining a general all-around fitness (I'd rather not stop running every other day if possible). Should I use only a 3x5 routine? 3x10? Oscillate between 3x5 and 3x10? Occasionally go for 3x1 or 3x3?
As an illustration, I can currently do 3x5 of 155 on the bench. If I up the reps, my form starts suffering on my last set. If I up the weight, I can't maintain a fluid motion and often can't lower the bar entirely to my chest. Or if I up the weight I can get maybe a few good reps out, but then I'm spent. Should I de-load and spend a few weeks just doing lots of reps of 135? Should I never train at 155, and instead vary every chest day with either lifting high reps at below 155 (say, 135) and low reps above 155 (say, 165)?
And, yeah, I eat a lot. I'm drinking about 4 gallons of milk a week in addition to many large meals per day.