http://www.tf2outpost.com/trade/10115470 got offered SF holy mackeral (6 keys)

http://www.tf2outpost.com/trade/10112331 Has a B/O of 7 keys 2 ref, also had offers that lead up to about 7 keys

http://www.tf2outpost.com/trade/10053988 got offers of SF sandvich (7-8 keys) or just 7 keys pure

http://www.tf2outpost.com/trade/10123668 Another B/O of 7 keys

http://www.tf2outpost.com/trade/10127246 B/O 7.5 keys

http://www.tf2outpost.com/trade/10105912 B/O 8 keys and he will give back 1 ref

http://www.tf2outpost.com/trade/9991698 Selling 2 for a big kill, big kill is valued at 15 keys so therefore he values his strange invis watches at 7.5 each

http://www.tf2outpost.com/trade/10083992 Got offered 6 keys (which is low but still proof)

As you can see by my proof it would be relatively easy to get a strange invis watch for under 8 keys so i don't think the price should go up to 8 keys rather bring it down to 7.5

http://www.tf2outpost.com/trade/10129545 Just sold his watch for 7 keys and 2.55 ref

http://www.tf2outpost.com/trade/10091104 unsold at 8

http://www.tf2outpost.com/trade/10112331 Another one selling for a bit under 7.5

The following links are all the posts on outpost that i could find unsold at 8 keys

http://www.tf2outpost.com/trade/10091104

http://www.tf2outpost.com/trade/10080141

http://www.tf2outpost.com/trade/10122448

http://www.tf2outpost.com/trade/10115599

http://www.tf2outpost.com/trade/10037288

http://www.tf2outpost.com/trade/10092313

http://www.tf2outpost.com/trade/9944236

http://www.tf2outpost.com/trade/10101877

http://www.tf2outpost.com/trade/10072844

some of these trades have only been up for a couple of hours but others have been up for up to a week and still haven't been sold