What has happened to my MR2 Spyder

My cars with good clutches do just fine going to high gears going slow, if there is not enough power to pull from that speed it just goes slower till it gets to higher rpm's. If its the clutch your clutch was going south anyway, 45mph going to 6th is not going to start a clutch problem. It needs looked over to now for sure, it could be other things, likely not related to your friend 's driving it, I had an older car I taught friend to drive a clutch with it took abused like you never thought, that original clutch was still going strong when I sold it, no telling the miles the odometer stopped working at 242k miles I estimate 320k as it was driven for another 7 years after odometer stopped working, then my brother drove it for another 2 years before he sold it and clutch was still working.

Did the engine rev up (rpm's go up) and car did not pick up speed (slipping) or did the engine bog down? If clutch was putting off so much smoke it must have been slipping and you should have noticed it slipping. Its going 35mph now is clutch slipping? If not then you likely have another issue. You need to get it looked over.

The SMT was a disaster. You are lucky it works at all.