A sampling as a starter. I listed first those recordings that have impressive sound and, except where noted, are very good performances. The Second listing I selected for the performances but noted where the sound was odd or not the best. If you have a particular composer you are looking for speak up. In general, most of what either Lopez Cobos, Erich Kunzel or Paavo Jarvi recorded on Telarc with the Cincinnati Symp Orch (or the Cin Pops Orchestra for the summer with Kunzel) have nice sound it is that Telarc sound if you like that. A lot of older stuff that I did not list is the music I consider to be incredible performances but the sound can suffer historical recordings on Testament, EMI etc. I like it and do not notice the sound problems after 2 minutes into the piece the performances simply take over - but I don't know that the recomendations would fit into your request.
I threw in a couple operas - Verdi's Il Travitoria and Wagner's Ring Cycle because in my opinion a lot of great 'classical' music is found in opera. I find the selections that I threw in to be particularly representative of the great classical music in opera.
(1) For quality of sound and performance: Mahlers 2nd - Fischer,on Channel classics; Mahlers 2 nd - Rattle, on EMI classics; - Ravel, Bolero etc Paavo Jarvi Cincinnati Symp on Telarc; Bach Haprsichord Concertos- Eggar Manze on Harmonia Mundi; Haydn String Quartets Op 76, The Lindseys on ASW; Beethovens 4 and 5 th Vanska BIS (very nice sound performance is not bad but not great); Mozart Violin concertos Manze Elgar harmonia mundi.
(2) For great performances Mahlers 9 th on DG Von Karajan BPO; Beethovens 9 symphony Box (from 1962) Dg Von Karajan BPO; Sibelius sym 4&7 EMI Von Karajan Philharmonia (sound is not the best but this is the recording upopn which Sibelius commented saying that Von Karajan understood his 4 th); Beethovens 9 th Furtwangler EMI (sound not the best but the performance is incredible and the sound is better than most other Furtwangler recordings, particularly those from during the war); Mozart Piano Concertos Uchida box set on Phillips, and box set on Sony by Perahia (as with any box set these two have hits and misses but the two artists present nice differences).; Haydn String quartets Op 20 quator mosaiques and same for op 33; Mendelssohn octet Nash Ensemble on Wigmore Hall; Mendelssohn violen concerto Kyung Wha Chung Decca Legends (the Decca Legends CDs have a certain sound I like it but you either will like it or hate it Chung does an incredible job though so you cant go wrong with this one and it will give you an idea of that Decca Legends sound); Keilberths Ring Cycle (Wagner) on Testament ( live from Beyreuth, the sound is not perfect but is not bad and the performance is excellent); Von Karajan DG Ring Cycle pretty much perfect; Bruckner 4 th symp. Wand RCA Red Seal; Bach St Matthew Passion, Klemperer EMI; Verdi Il Trovatore Von Karajan EMI