How to spot a high current amps?

Hmm. I have amps with current rating, eg., 45 amps, 40 amps, 60 amps. One of them is not difficult at all to lift. Very light in fact, an old Mission Cyrus One integrated that feels like it weighs a pound or two. Yet it was rated at 40 amps, but only 25 wpc. Now, I'm sure you think that's just marketing talk, but the fact is that I used to drive a pair of KLH 5's with it(about 77db efficiency) and it's never had trouble with any pair of speakers. It is a little light on the very bottom, a little warm in the upper bass and seriously rolled off in the treble, but still a very musicallly dynamic little amp.

In general, however, the heavier amps do seem to be rated for higher current.

Ghostrider, the rating and advertising claim is "capable of 40 amps pk-pk," and the claimed continuous wpc number into 8 ohms both channels driven is 30. This amp was actually one of the first I saw, this was 20 years ago, for which any current delivery claim was made. The point was it actually was a very robust little amp had not trouble driving very inefficient speakers that supposedly higher powered amps could not drive. So there must have been something to their claims. Nowadays, I use larger amps designed for high current delivery and stability into any load designed by people who I have spoken with and trust.