Firstly my pc specs are below, in the small print, right at the bottom of this post.
1 - I am working on a highly detailed biggish map and so far I'm getting 40-50fps with everything on highest.
2 - Level planning plan a big part in speed and framerate, as does collision mode, box collision is by far the quickest.
3 - Use of scripting can increase speed, goindoors.lua for inside buildings will increase framerate, from 60fps to around 150fps, sometimes 200+fps
4 - As Disturbing13 has pointed out there are constant updates and improvements to GG and there are a LOT to come in the future.
5 - Add to that the great dev support and some extremely talented users here, and you have a great program to use and be part of.
Hopefully that helps you Sheogorath. Just take a look in the store and see what people have created. Low poly models and Music, SFX that looks and sounds great. I have put 380+ hours into GG and I plan to put in a lot lot more too.
Aftershock Quad Core AMD FM2+ 3.5 GHz 8GB Motherboard and Processor, A7700k apu, AMD HD7870 gfx card.
King Korg Synth, Alesis SR18 Drum Machine, Akai MPX8 sample player, Roland Fantom XA Synth, Axus Digital AXK2 Digital Drum Kit.