I've identified 3 key years of the Silver Panda for analysis. 1995 Small Twig Micro, 1999 Serif, 2000 Frosty and 2000 Mirror. New collectors or collectors looking for good deals without overpaying would compare how much premium they are paying for a double-sealed coin over a coin in capsule, a graded MS69 over a coin in capsule, a graded MS69 over a double-sealed etc. There are some collectors who would also place a percentage premium based on whether it is MS69, 68 or 67.
With price data from US ebay transacted prices collected from Dec 2010 to Nov 2011, I could present some figures indicated how these coins could compare and how much premium has been paid. The most readily available data is actually that of the 2000 Frosty as it is the most heavily transacted amongst the key dates.
2000 Frosty
The average price transacted for a 2000 Frosty in capsule range between US$175 to US$340 while a double-sealed was between US$202 to US$391. Percentage premium of double-sealed over capsule is between 15.5% to 39.5%
% premium of MS69 / Capsule: 53 - 118%
% premium of MS68 / Capsule: 21 - 64%
% premium of MS67 / Capsule: -18 - 36%
% premium of MS66 / Capsule: -12 - 17%
% premium of MS69 / DS*: 10 - 66%
% premium of MS68 / DS*: -13 - 19%
% premium of MS67 / DS*: -41 - 5%
2000 Mirror
For 2000 Mirror, there are only 2 sets of data to look at for same month of transaction. That is to say, only in the month of May and October, we have data to compare for premium of NGC MS69 & MS68 over double-sealed coins.
% premium of MS69 / DS*: 176 - 191%
% premium of MS68 / DS*: 88 - 129%
1999 Serif
% premium of MS69 / DS*: 60 - 363%
% premium of MS68 / DS*: 5 - 193%
% premium of MS67 / DS*: 41%
1995 Small Twig Micro
% premium of MS69 / DS*: 75 - 153%
*DS denotes Double-Sealed
In conclusion, a graded coin has different percentage premium for different year due to it's mintage, NGC graded population for that grade and even silver spot price. The relation is not as linear as MS69 indicates 100%, MS68 - 50% and so on. For example, the 1992 Large Date would have much more graded MS69 and above compared to the 1992 Small Date due to its eye appeal and hence collectors are willing to pay 30 - 40% more for the Small Date MS69. A 2011 MS70 Early Release could fetch a 100% premium over capsuled one while the MS69 would be priced nearly the same as the capsuled.
Silver spot price could affect the premium in the sense that when silver spot is high, collectors would settle for something lower grade like MS67 or capsule coin.