What can I expect performance wise woth an R8000?

Hello
 

I am new to the world of flashing routers and I very much would
appreciate help and advice on the potential download speeds of a
Netgear R8000 router.  I am hoping to turn the router into a VPN
Client and would like to know its potential download speeds when
encrypting the internet?
 

For the last couple of years I have been using a VPN service, not
for anything bad.  I just want to maintain my privacy while
surfing the internet.
 

Normally I used my computer, with the VPN provider's software, to
encrypt all my internet surfing.  Seeing as I am a cable
subscriber I get 70Mb/s download speeds and when I encrypt my
connection to the internet this drops marginally, if at all.
 

However a few weeks ago I experimented with making a router as a
VPN Client, so I bought a Linksys E4200 router and flashed DD-WRT
onto it.  I have to say that I have no experience in the IT
world apart from what I learn from Mr Google. 
 

I was exceptionally pleased with my progress and was able to turn
my router into a VPN Client.  However I was not happy with the
download speeds falling to between 4Mb/s and 8Mb/s considering that I
am paying for 70Mb/s.  I soon discovered that the poor little
processor within my router just was not up to the job and was working
as hard as it could at encrypting my internet surfing.
 

I then bought a Linksys 3200ACM and had a go at flashing DD-WRT
onto the router.  Once again I was successful at flashing the
router and turning it into a VPN Client.  I was also happy with
the increased download speeds that ranged from 15Mb/s to 35Mb/s. 
I don't know why there was such a big difference but I was happy. 
Sadly the WiFi was awful and kept breaking every few minutes so I
sent the router back.  No point having a WiFi router if the
radio does not work.
 

And here we come to the question, if I was to buy and flash a
Netgear R8000, and turn the router into a VPN Client what sort of
encrypted download speeds would I hope to expect?
 

Would the speeds be similar to the Linksys router considering both
routers have similar specced processors?
 

Sorry for such a long winded question, but I wanted to give a
little background on my limited experiences and knowledge.