Holy crap I love Deep Purple. Top 3 band for me that probably just beats out Dream Theater.
Ian Paice, Jon Lord and Ritchie Blackmore make my all-time top 1 or 2 respective drummers, keyboardists and guitarists. I really believe that Dream Theater modelled their configuration after the Mark II lineup. Aside from being a 5-piece with keyboards and superb musicianship, both bands manage to instill a lot of nuance and finesse in their brand of hard rock/heavy metal. And that core of Paice/Lord/Blackmore which lasted through Marks I-III is reminiscent to me of DT's Petrucci/Myung/Portnoy.
Funny thing too is that both DP and DT are accused of wankery, although of different sorts. Purple are steeped in 70's hippie-bluesy jam improvisation, a style which completely satisfies my love of both hard rock and jam-rock. If you listen closely to those short-ish songs on In Rock and Machine Head, they're practically lightly-pencilled sketches that provide a vehicle for the band to fill in the blanks by flexing their muscles and showing off their instrumental chops. Songs like "Lazy", "The Mule" and "Space Truckin" are obviously designed with extended jams in mind. Those sketches become full-fledged paintings on Made In Japan, the best live album ever imo. It's no wonder that DT did a Ytsejam cover of that album.