The D5100 is no match for the D3s, D4, or D800 but I think it would be better for wedding work than a D2x. I am not knocking the D2x, but it has had it's day. Both the 24MP D3200 and 16MP D5100 have a much higher DXO Sensor rating than the D2x
At 6400 the D5100 shows a low amount of noise + it has built in flash. I would shoot with an AF-S 80-200 or 70-200 f/2.8 lens, although a 28-70 or 24-70 could be used.. The swivel LCD would be very useful for shooting over crowds. The HD1080P at 30fps Video is quite good. The D5100 is also a better travel camera.
I just checked your profile. Just take your D3200 for your travel, but also bring your 24-70 as it could be used inside buildings without flash.