The best tubes that I ever used in my Belles preamp were the Mullard CV4003 from Upscale Audio. The platinum grade are only $40 each.
Of the two you mention above, I would try the JAN Philips 5814. Swapping tubes in the Belles is very easy and only takes a few minutes...go for it!
Of the two you mention above, I would try the JAN Philips 5814. Swapping tubes in the Belles is very easy and only takes a few minutes...go for it!