Currently, you can see in the widget:
1. total number of the site ever
2. total visitors today
3. how many users are currently online
and much more if you want.
But in the admin, you can not see the total number of visitors for a full year. It's a good idea and I'll include it in the next version 1.1 as well as those of last year.
These SQL queries are not those who consume lots of CPU time because it is the more simple to be done to a server.
Compared to the current version 1.0.10, it will create 8 additional queries (out of 33 existing), an increase of 25% load. By putting only the current year, it will create 4 additionals queries, an increase of 12.5% load.
With the new account of "visitors feeds" introduced by the forthcoming version 1.1, then there will be 49 queries.
In comparison, all versions of WordPress make 109 queries in the overview page to display 20 days in a graph. For a graph of 30 days they made 149 queries. For a graph of 50 days, they made 229 queries.
Statpress visitors display a graph in 4 queries regardless the number of days displayed.
Then you see, Statpress Visitors is more faster.
I look the ks_stats reloaded data tables and these data tables are not compatible with the other fork of statpress, my apologize.
But as these data tables have not the same name, there is no compatibility issues. You will start only at 0.