this.elem and this.options can be cached earlier

also try to reduce number of var declarations

src/effects.js

@@ -406,58 +406,61 @@ jQuery.fx.prototype = {
 
 	// Each step of an animation
 	step: function( gotoEnd ) {
-		var t = jQuery.now(), done = true;
+		var t = jQuery.now(), 
+			done = true,
+			elem = this.elem,
+			options = this.options,
+			i, p;
 
-		if ( gotoEnd || t >= this.options.duration + this.startTime ) {
+		if ( gotoEnd || t >= options.duration + this.startTime ) {
 			this.now = this.end;
 			this.pos = this.state = 1;
 			this.update();
 
-			this.options.curAnim[ this.prop ] = true;
+			options.curAnim[ this.prop ] = true;
 
-			for ( var i in this.options.curAnim ) {
-				if ( this.options.curAnim[i] !== true ) {
+			for ( i in options.curAnim ) {
+				if ( options.curAnim[i] !== true ) {
 					done = false;
 				}
 			}
 
 			if ( done ) {
 				// Reset the overflow
-				if ( this.options.overflow != null && !jQuery.support.shrinkWrapBlocks ) {
-					var elem = this.elem,
-						options = this.options;
+				if ( options.overflow != null && !jQuery.support.shrinkWrapBlocks ) {
 
 					jQuery.each( [ "", "X", "Y" ], function (index, value) {
 						elem.style[ "overflow" + value ] = options.overflow[index];
 					} );
 				}
 
 				// Hide the element if the "hide" operation was done
-				if ( this.options.hide ) {
-					jQuery(this.elem).hide();
+				if ( options.hide ) {
+					jQuery(elem).hide();
 				}
 
 				// Reset the properties, if the item has been hidden or shown
-				if ( this.options.hide || this.options.show ) {
-					for ( var p in this.options.curAnim ) {
-						jQuery.style( this.elem, p, this.options.orig[p] );
+				if ( options.hide || options.show ) {
+					for ( p in options.curAnim ) {
+						jQuery.style( elem, p, options.orig[p] );
 					}
 				}
 
 				// Execute the complete function
-				this.options.complete.call( this.elem );
+				options.complete.call( elem );
 			}
 
 			return false;
 
 		} else {
-			var n = t - this.startTime;
-			this.state = n / this.options.duration;
+			var n = t - this.startTime,
+				specialEasing, defaultEasing;
+			this.state = n / options.duration;
 
 			// Perform the easing function, defaults to swing
-			var specialEasing = this.options.specialEasing && this.options.specialEasing[this.prop];
-			var defaultEasing = this.options.easing || (jQuery.easing.swing ? "swing" : "linear");
-			this.pos = jQuery.easing[specialEasing || defaultEasing](this.state, n, 0, 1, this.options.duration);
+			specialEasing = options.specialEasing && options.specialEasing[this.prop],
+			defaultEasing = options.easing || (jQuery.easing.swing ? "swing" : "linear");
+			this.pos = jQuery.easing[specialEasing || defaultEasing](this.state, n, 0, 1, options.duration);
 			this.now = this.start + ((this.end - this.start) * this.pos);
 
 			// Perform the next step of the animation