I noticed new suggestion in R# 5.0 which suggest me to convert for-loop into foreach-loop for my array.
There are performance penalty in such suggestion (you can check yourself). Look at Kevin Ransom: To foreach or not to foreach that is the question.
"Recently email was forwarded to me with a link to a page with some performance tips for developers. The second performance tip on the page was:
foreach through an array is incredibly slow compared to for (int i = 0; i < array.Length; i)
This one leapt out at me because it is well ... not to put too fine a point on it ... wrong! (at least that is what I thought). C# and Visual Basic 7 both contain specific optimizations to ensure that foreach on arrays perform equivalently to for(int i=0; i < array.Length; i); I have written plenty of code assuming foreach and for(int i; ...) were equivalent. To verify my assumption and to ensure that the code I wrote was as efficient as possible in the future I did a little experiment: I wrote a small C# application with 2 functions the first of which enumerated an array of integers using foreach, the second enumerated an array of integers using for(int ...). I then used ildasm to disassemble the compiled binary to IL and then examined the resulting code."
You may also read Patterns & Practices: Improving .Net Application Performance
"Use for Instead of foreach in Performance-Critical Code Paths
Use for instead of foreach (C#) to iterate the contents of collections in performance-critical code. foreach in C# and For Each in Visual Basic .NET use an enumerator to provide enhanced navigation through arrays and collections. For more information, see "Enumeration Overhead" in the "Collection Guidelines" section later in this chapter."
Аlthough I quoted very old topics they still valid in general. You can find many posts on this topic in Internet. Maybe you will interest in discussion here: For vs Foreach loop in C#
Of course there are many nuances, but I suggest in general make additional check and do not suggest this conversion for arrays (or similar operation context) but still suggest for other collections.