A few words about strength of play

I am well aware that there are people, who like to use ChessBot in "Bot vs Bot" games. So it is pretty frequent question - how to make ChessBot to play as strong as possible.

It is not so simple question however. There are many factors and parameters, which affect on how strong your chess bot will be.

First of all,
it depends on how good hardware you have
(escpecially CPU and RAM). Stockfish on intel pentium 4 will be much weaker than on intel i7.

Secondly, many depends on chess engine. Latest versions of Stockfish (and its clones like Brainfish, Asmfish, Sugar), Houdini and Komodo are considered the strongest engines in the world at this moment. Here is rating list: http://www.computerchess.org.uk/ccrl/4040/rating_list_all.html

Thirdly, very improtant is what
opening and endgame books
you're using. I can recommend to try latest Brainfish engine with Cerebellum opening book, here is official website: http://www.zipproth.de/

Endgame book (aka EGTB - endgame tablebases) can be for 5,6 or even for 7 pieces. I can recommend to try Syzygy 5-men tb, read  more about it and download here: http://kirill-kryukov.com/chess/tablebases-online/

Also strength depends on chess engine configuration. Many chess engines have such parameters as Threads (how many CPU cores use to calculate moves), Contempt (it's something like aggressiveness of play style), Hash size and many others. If you want to know more about it, here is good website: https://chessprogramming.wikispaces.com/

Always set Threads parameter to a max value in engine's settings (it is set to 1 by default). For example, if you have 4-core CPU, set Threads = 4, etc.

Use 64-bit versions of engines, instead of 32-bit versions, if possible (you need 64-bit Windows for that).

And there is one more important moment - time management. Chess engine can play by time or by fixed depth. Classic ChessBot supports only "play by depth" method (it has "floating depth" feature, but still). New ChessBotX supports "play by time" feature, please read more here about it.
Always use "play by time", when you need to achieve the strongest play.

Also it is strongly recommended to use "Permanent brain" feature (pondering). This option allow engine to calculate next move during the opponent's turn, which allow to increase overall strength of play by 15-30%. ChessBotX versions 1.2 and higher support this feature.

Of course
do not use delays
in "bot vs bot" games. Also
do not use "Simulate human moves"
option. Also you can make ChessBot a little faster by experimenting with system delays.

Turn off animations at website settings if possible. Also try to decrease size of the chess board if possible (you can even try to lower your screen resolution for that). These recommendations will help the bot to react faster.