1) Absolutely. As comparable as say Green Irish Tweed and Cool Water. Clearly loads of similarity.
2) Floris Santal = Guccy Envy minus the ginger note. They have the same synthetic sandalwood base. If the ginger turns you on, go for Envy. If it turns you off, go for Santal.
And yeah, I wouldn't wear these scents in the summer heat.