Rask literally has some of the best playoff stats ever
Top goalies by playoff SV% over the past 5 years (min 15 GP)...
1. Craig Anderson - .932 SV%, 2.11 GAA, 13-10
2. Braden Holtby - .928 SV%, 2.04 GAA, 35-26
3. Martin Jones - .926 SV%, 2.07 GAA, 22-18
-- Ben Bishop - .926 SV%, 2.09 GAA, 21-13
5. Matt Murray - .923 SV%, 2.08 GAA, 28-15
-- Hendrik Lundqvist - .923 SV%, 2.28 GAA, 31-28
7. Jake Allen - .922 SV%, 2.10 GAA, 9-10
-- Carey Price - .922 SV%, 2.20 GAA, 16-14
-- Connor Hellebuyck - .922 SV%, 2.36 GAA, 9-8
-- Marc-Andre Fleury - .922 SV%, 2.37 GAA, 30-24
-- Cam Talbot - .922 SV%, 2.48 GAA, 7-7
12. Andrei Vasilevskiy - .919 SV%, 2.68 GAA, 15-11
13. Tuukka Rask - .916 SV%, 2.38 GAA, 14-16
14. Pekka Rinne - .915 SV%, 2.46 GAA, 30-25
--- Corey Crawford - .925 SV%, 2.47 GAA, 27-22
Same thing, but regular season and min 100 GP...
1. John Gibson - .923 SV%, 2.29 GAA, 93-55-20
-- Carey Price - .923 SV%, 2.34 GAA, 141-84-23
3. Antti Raanta - .922 SV%, 2.29 GAA, 68-40-15
-- Corey Crawford - .922 SV%, 2.35 GAA, 147-81-26
5. Sergei Bobrovsky - .921 SV%, 2.42 GAA, 155-95-20
-- Roberto Luongo - .921 SV%, 2.43 GAA, 123-87-33
7. Tuukka Rask - .920 SV%, 2.30 GAA, 172-92-37
8. Ben Bishop - .919 SV%, 2.30 GAA, 156-80-26
-- Braden Holtby - .919 SV%, 2.41 GAA, 188-73-31
-- Marc-Andre Fleury - .919 SV%, 2.41 GAA, 155-78-31
-- Semyon Varlamov - .919 SV%, 2.68 GAA, 126-92-23
12. Jonathan Quick - .918 SV%, 2.24 GAA, 144-95-27
--- Pekka Rinne - .918 SV%, 2.38 GAA, 158-80-32
--- Devan Dubnyk - .918 SV%, 2.42 GAA, 154-93-25
--- Cam Talbot - .918 SV%, 2.50 GAA, 127-95-21
--- Frederik Andersen - .918 SV%, 2.55 GAA, 148-63-31
To provide better context to the actual cap figure... the 5.75-mil he signed for previous accounted for 8.33% of the 69.4-mil cap at the time. The 7.00-mil he just re-signed for accounts for 8.81% of the current 79-mil cap. So we're talking half a percentage point difference in relative value to the salary cap, which is pretty minor.
Edit: Also, as you can see from the numbers above, the notion of elite goaltenders in today's NHL is a virtual myth. There are 35 goalies within 1% SV% (0.010) of the top guys. Put any behind a good defensive team and they're going to post elite numbers; but them behind a team that disregards defense, and they'll look fairly average. Fleury is a perfect illustration of this - his first season away from the "always offense-first" Penguins and he plays way above his career average.