Update:
I visited Audio Planet yesterday afternoon with the intention to finalize the Monitor Audio's M4. I felt with Tannoy V4 having the bass reflex port only at the back, it may be a little bit of a problem as the kind of (fixed) speaker placement options I have - the speakers will have only 8-10 inches gap from the rear wall and also not much breathing space on the sides. So I spoke to Palani about the M4 & M6 and how they compare against each other. Had very little time to do a proper audition - but I must say with one additional driver, M6 surely sounded 'audibly' better than the M4 (which is expected anyway), though I was not sure if it was worth 10k extra cost (this is a compliment for M4, really). Palani thought it was and strongly recommended to me to spend the extra money for what he thought was a 'step up' from M4.
So, after some serious thinking - I decided to go ahead and buy the M6. I carried those two gigantic boxes in my car yesterday and got them home. Set those up and played some music - mainly some Jagjit/Chitra Singh, Ghulam Ali Ghazals, some hindustani classical and some of my current Bollywood favourites like Guzarish, 3Idiots etc.
I must say - I loved the sound of the M6. The vocals and the instrumentals (especially traditional Indian instruments like Sitar, Sarod & Tabla) sound brilliant. From what I remember - Wharf 9.6 was the only other speaker which really fascinated me in stereo music - and it was surely more bright - but M6 sounds more soothing (& not really bright), to my ears.
I am told the speakers would 'open up' a little more after 10-20 hours of initial use. If that happens, its great. Even otherwise - I am feeling good that I went for the M6 instead of M4, by stretching my budget.
And sincere thanks to all of you for all your inputs and especially to those who suggested me to check out the M6.
-- Saumitra